1. Field of the Invention
The present invention relates to a low tension dual helical conveyor systems capable of conveying articles along concentric helical paths having mutually opposite directions of travel.
2. Description of the Related Art
Endless conveyors of the type contemplated herein generally include an endless conveyor belt which has sufficient flexibility to allow the belt to travel over concentric helically shaped paths having opposite directions of travel from a product input station to a product discharge station. Since the path is helical, the belt must be capable of flexing at least to a limited extent along at least three mutually orthogonal axes in order to permit the belt to follow such a relatively complex path. With concentric helical paths, the flexibility of the belt along several axes is increasingly significant, particularly when the helical paths are connected by a cross-over section of conveyor belt.
In order to permit such multi-directional flexing, such conveyor belts are generally constructed of a plurality of interconnected links which permit at least limited link-to-link articulation along two or more mutually orthogonal axes. In such instances, the links are generally constructed of materials such as steel, plastics, combinations thereof or the like, making the weight of the belt a relatively significant factor in operating the conveyor system.
Conveyor belts of the type contemplated herein generally range from about 12 inches to about 60 inches in width, and above about 200 feet in length. Although single helical conveyors generally may be of length up to about 5,000 feet, the possible length of such conveyors is virtually unlimited. When a conveyor belt is constructed of numerous interlocked steel links and is between 12 and 60 inches in width and more than 200 feet in length, the substantial weight of the belt becomes a significant factor to reconcile. For example, the belt must be driven through the work path which begins at the product input station and ends at the product discharge station. Thereafter, the belt enters the return section where it reverses direction and re-enters the product input station to continue operating in its endless path. In helical conveyors, the belt is driven up a helical shaped path in an up-go conveyor, and down a helical shaped path in a down-go conveyor.
In certain systems, such as the dual concentric conveyor systems disclosed in U.S. Pat. Nos. 3,664,487 and 4,036,352, the belt is driven by positive drive forces provided by drive members such as rotating drive angles driven on one side of the helical loops. In other systems in which a single helical path is defined, the belt is driven by friction forces imparted to it along the inner edge by a circular shaped rotating cage having friction/slip members attached to it and around which the belt is wrapped in the work zone. When the belt is friction driven, it generally is also provided with additional assistance by a motor driven sprocket which is constructed and arranged to engage the links of the belt directly as it is rotatably driven by the assist motor. Such motor assist is particularly needed in up-go helical conveyors where the relatively heavily weighted belt is made to traverse an up-go helical path against the force of gravity. A motor driven assist sprocket is also utilized in helical shaped down-go conveyors, although the gearing and roller arrangements differ somewhat from the up-go conveyors, and the assist force required is somewhat different.
In general, positively driven belts are subjected to greater tensile forces then the belts which are driven by friction forces due in part to the fact that the friction drive surface is generally moving at a faster rate of speed than the rate of speed of the driven edge of the belt. For example, when a friction driven belt of about 36 inches in width travels one revolution, the friction drive mechanism will travel approximately 36 inches further than the corresponding driven edge of the belt.
Conveyor belts of the type contemplated herein are generally used for conveying products under various conditions. For example, in some applications, the belts are used to convey dough products through relatively high temperature atmospheres in order to assist the dough in rising prior to formation of a bread product. In other applications, the belts may be made to carry food products through relatively cold atmospheres, sometimes under freezing conditions. In still other applications, the belts may be required to conduct products at room temperature.
In each instance, the belt, being made of a plurality of interlocked metal links, will react to the surrounding conditions such as temperatures, cleanliness and the like, with the result that the belt will undergo a natural stretch or compression. Such factors will, in turn, affect the belt tension. For example, some instances, the belt will become longer during operation and, in others, the belt may become shorter. Such variations sometimes make it relatively difficult to drive the belt by friction drive devices, since positively driven systems are relatively less complicated to control.
Dual concentric helical conveyor systems of the type disclosed in U.S. Pat. Nos. 3,664,487 and 4,036,352, which are positively driven, generally utilize conveyor belts which are permanently curved to meet the curvature of the helical conveyor paths and to accommodate the positive drive systems. In such instances, the permanent curvature in the belt also accommodates the transitional portionxe2x80x94or cross-over sectionxe2x80x94which connects both main conveyor systems. Further, the permanent curvature accommodates the positive drive mechanism by providing relative synchronized precision between the positive drive mechanism and the belt in both of the main conveyor sections.
Positively driven dual concentric helical conveyor systems have a number of disadvantages. For example, the preset curvature in the belt limits the location and angle of the xe2x80x9cproduct infeed/product dischargexe2x80x9d sections. Also, the preset curved nature of the belt prevents reversing the belt to reduce wear and increase belt life. Moreover, the significant tension to which the belt is normally subjected by the positive drive mechanism tends to increase belt wear and limit belt life. We have invented a dual concentric conveyor belt system which incorporates low tension friction drive systems in both of the main conveyor sections which permits the use of a normally straight flexible conveyor belt. In addition, we have invented a low tension friction drive system which can be incorporated into the cross-over section of the main conveyor sections in a manner to communicate the main conveyor sections with a low tension friction drive system, independent of whether the main sections are driven by friction or by positive drive devices, all while reducing the wear on the conveyor belt.
The invention relates to a dual helical conveyor system, which comprises a conveyor belt adapted to move in a first direction along a first helical path and thereafter in a second direction generally opposite the first direction along a second helical path inside the first helical path. Preferably the first and second helical paths are generally concentric. The conveyor belt is further movable through a cross-over section along a cross-over path connecting the first and second helical paths. A conveyor belt drive mechanism is provided in the cross-over section to frictionally drive the conveyor belt along the cross-over path and between the first and second helical paths. The conveyor belt is driven by a first friction drive mechanism along the first helical path, and a second friction drive mechanism along the second helical path. The conveyor belt defines a product input/discharge section at at least two locations, and a conveyor belt return device is provided to guide the conveyor belt between the first and second helical paths. The conveyor belt return device comprises a generally circular shaped guide member mounted for rotation at a location between the product input/discharge sections to guide the conveyor belt therebetween.
The first friction drive mechanism comprises a first rotatable drive cage positioned adjacent an inner edge of the conveyor belt along the first helical path, the first drive cage having first friction drive devices attached thereto and positioned in engagement with the inner edge of the conveyor belt to frictionally drive the conveyor belt along the first helical path. The second friction drive mechanism comprises a second rotatable drive cage positioned adjacent an inner edge of the conveyor belt along the second helical path, the second drive cage having second friction drive devices attached thereto and positioned in engagement with the inner edge of the conveyor belt to frictionally drive the conveyor belt along the second helical path. The first and second friction drive devices on the first and second rotatable drive cages are preferably made of resinous material, preferably ultra high molecular weight polyethylene.
Preferably, the first and second drive cages are independently driven by respective power drive systems, and each power drive system comprises a power drive device having a cage drive member connected thereto to rotatably drive an associated drive cage. The cage drive members each comprise a link chain which is driven by the respective power drive system. Although each power drive device is preferably driven by an electric motor as will be disclosed herein, alternatively other known power drive systems such as hydraulically powered drive systems or the like may be utilized.
The conveyor belt drive mechanism adjacent the cross-over path comprises a plurality of friction driven members positioned in moving frictional engagement with an edge portion of the conveyor belt along at least a portion of the cross-over path to frictionally drive the conveyor belt between the first and second helical paths. The friction drive members are preferably made of resinous material, preferably ultra high molecular weight polyethylene.
The conveyor belt drive mechanism adjacent the cross-over path comprises a link chain adapted to move along an endless path adjacent the cross-over path, and the ultra high molecular weight polyethylene friction drive members are attached to the movable link chain.
In a preferred embodiment, a dual helical conveyor system is disclosed which comprises an endless conveyor belt adapted to move in a first direction along a first helical path portion and thereafter in a second direction generally opposite the first direction along a second helical path portion inside the first helical path. Preferably the first and second path portions are generally concentric. Movable friction/slip drive devices are positioned in engagement with an inner edge portion of the belt in the first helical path portion, and movable friction/slip drive devices are positioned in engagement with an inner edge portion of the conveyor belt in the second helical path portion. The conveyor belt is further movable along a cross-over path which connects the first and second helical paths, and a conveyor belt drive mechanism is positioned adjacent the cross-over path. The conveyor belt drive mechanism includes movable friction/slip members positioned in engagement with an inner edge portion of the conveyor belt in the cross-over section to provide force sufficient to assist movement of the conveyor belt between the first and second helical paths.
According to one embodiment, the dual helical conveyor system comprises a first helical conveyor section having a first conveyor belt adapted to move in a first direction along a first helical path, and a second helical conveyor section having a second conveyor belt adapted to move in a second direction opposite the first direction along a second helical path and located inside the first helical path, preferably concentric therewith. Each of the first and second conveyor belts have associated therewith a friction drive mechanism which comprises a rotatable cage having friction drive members attached thereto and positioned in moving frictional/slip engagement with an inner edge portion of the associated conveyor belt to drive the associated conveyor belt along the respective helical path. Each of the first and second helical conveyor sections include a product input/discharge section for receiving and/or discharging products in dependence upon the direction of the respective conveyor belt. The system further comprises a third conveyor section extending between the product input/discharge sections to convey products therebetween. The third conveyor section preferably has an arcuate configuration and is positively driven by positive drive members. Alternatively, the third conveyor section may be driven by a friction drive device having a plurality of friction/slip drive members in movable engagement with an edge portion of the conveyor section. The friction drive device associated with the third conveyor section preferably comprises a link chain having a plurality of friction/slip drive members attached thereto and positioned in movable engagement with the edge portion of the third conveyor section.
In another embodiment, the dual helical conveyor system comprises a first helical conveyor section having a first conveyor belt adapted to move in a first direction along a first helical path, and a second helical conveyor section having a second conveyor belt adapted to move in a second direction opposite the first direction of the first belt along a second helical path inside, but preferably concentric with the first helical path. Each of the first and second conveyor sections are independently driven by respective independently controlled friction drive mechanisms and have respective product input/discharge sections. A third conveyor section is positioned and adapted to carry products between the product input/discharge sections of the first and second helical conveyor sections. The third conveyor section preferably has an arcuate configuration and a friction/slip drive mechanism is provided to drive the conveyor section. Alternatively, a positive drive mechanism may be provided to drive the third conveyor section.